There are many factors that can influence the outcome of a caries experiment in animals. Included in these are the age and physical health of the animal, physical conditions of the animal housing facilities, types of treatments being tested, method used in scoring dental caries, and the experience and expertise of the person scoring caries in these animals. In this investigation the effects of the scoring method and reproducibility of the examiner using each method were studied to see how significant a role these factors play in such animal experiments. The original method of Keyes and a modification of this method were compared in two separate studies at NIDR. Experienced examiners participated in each study and replicate examinations of the smooth surfaces of the animal jaws were conducted. In each study the results showed the examiners were able to achieve high values of reproducibility using either method in scoring dental caries in rats. Differences between groups were slightly different for the two methods, but with no consistent pattern and of no practical significance.